46 University of California Puhlications in Botanii [Vol.8 



compact, more or less parallel, not at all or but slightly branched, 

 arising from basal filaments on the surface of the host and extending 

 away from it, and with the gonidangia on the outer free ends. 



Key to the Species. 



1. Gonidangia simple, each terminating a trichome 2 



1. Gonidangia compound, i. e., in groups within a common sheath 



4. R. epiphytica (p 49) 



2. Gonidangia spherical to ovoid 3 



2. Gonidangia hemispherical 3. R. clavata (p 48) 



3. Gonidangia splicrical to ovoid, 8-9/* in diam 1. R. Laminariae (p 46) 



3. Gonidangia spherical, 4-6/a in diam 2. R. subimmersa (p 47) 



1. Radaisia Laminariae S. and G. 



Plate 3, figs. 14-16 



Prostrate portion of the plant consisting of compact, radiating 

 filaments, dichotomously or subdichotomously branched, forming a 

 closely compact thallus circular in outline, up to 300/* diam. ; cells 

 of prostrate filaments quadrate, 4-4. 5/a diam., giving rise by horizontal 

 divisions to closely compact, erect filaments ; the whole thallus 30-40a 

 thick ; gonidangia terminal on the erect filaments, spherical, or slightly 

 oval, 8-9/u. diam. ; gonidia 0.8/* diam. formed by simultaneous division ; 

 color bright blue-green. 



Growing on the terminal portion of the blades of Laminaria Sin- 

 clairii. Fort Point, San Francisco, California. This locality, so far 

 as we know, is the only one in which this species has been observed. 

 It probably has a much wider distribution. The host plant extends 

 from Vancouver Island, British Columbia, to the vicinity of Point 

 Conception, California. 



Setchell and Gardner, in Gardner, New Pac. Coast Alg. II, 1918, 

 p. 444, pi. 37, figs. 14-16; Collins, Holden and Setchell, Phyc. Bor.- 

 Amer. (Exsicc), no. 2254. 



Radaisia Laminariae we have taken to represent a typical form of 

 the genus, having a single layer of cells for the base which gives rise 

 to perpendicular, parallel, unbranched filaments extending away from 

 the host, and each bearing a single terminal gonidangium. The whole 

 cushion or colony is in reality a single plant resulting from the growth 

 of a single gonidium. The plants of this species start from a single 

 cell, and by a few divisions a small group of cells is formed ; around 

 the margin the cells begin to arrange themselves radially in rows, 

 and by divisions in two planes; radial and tangential, a circular disk, 

 one layer of cells deep, is formed. The marginal cells enlarge tan- 



